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Big Picture on Thinking

The human brain may be the most complex structure in the universe. It is so powerful that it is attempting to understand itself, through research.

New techniques have opened up ways of exploring the brain. Functional imaging allows us to watch the brain in action; our understanding of the biochemistry of nerve function has blossomed; and the genetic revolution has allowed us to probe the function of individual genes and proteins. These techniques are shedding light on the very essence of human life - how we feel, think and act. Even the nature of consciousness is beginning to be unravelled. But:

Can we really see ourselves simply as 'biological computers'?

If we understand the basis of our mental self-image, or identity, can we (and should we) seek to change ourselves into something else?

And if our actions are just biology in action, how responsible can we be for what we do?

The human brain may be the most complex structure in the universe. It is so powerful that it is attempting to understand itself, through research.

New techniques have opened up ways of exploring the brain. Functional imaging allows us to watch the brain in action; our understanding of the biochemistry of nerve function has blossomed; and the genetic revolution has allowed us to probe the function of individual genes and proteins. These techniques are shedding light on the very essence of human life - how we feel, think and act. Even the nature of consciousness is beginning to be unravelled. But:

Can we really see ourselves simply as 'biological computers'?

If we understand the basis of our mental self-image, or identity, can we (and should we) seek to change ourselves into something else?

And if our actions are just biology in action, how responsible can we be for what we do?

Vision, memory and how our eyes play tricks on us2–3Mood, emotions, personality and feelings4–5Consciousness and self-identity6–7Understanding other people (and ourselves)8–9How free is free? Controlling our actions10–11Real voices: Life with synthaesthesia and schizophrenia12–13New knowledge, new issues14–15The big picture16

FIND OUT MORE

ISSUE 4

SEPTEMBER2006

THINKING

An invisible gorilla?

Find out on page 3.

Now you see it...Optical illusionssuch as this helpus understand howthe brain works.

It is so powerful that it isattempting to understand itself,through research. The task is daunting. Someneuroscientists say that if thebrain were simple enough to beunderstood, we would not beclever enough to understand it. Yet the nature of humanexistence has fascinated usfor centuries. It used to be

philosophers

who held swayon the nature of human life,the mysteries of consciousness,and other Big Questions.In the past 20 years, though, abattery of new techniques hasopened up new ways of exploringthe brain.

Functional imaging

allows us to watch the brain inaction; our understanding of the

biochemistry of nerve function

has blossomed; and the

geneticrevolution

has allowed us toprobe the function of individualgenes and proteins. These techniques are sheddinglight on the very essence of human life – how we feel, howwe think and how we act. Eventhe most difﬁcult question of all,the nature of

consciousness

,is beginning to be unravelled.While exciting, thesedevelopments also raise unease.Can we really see ourselvessimply as ‘biological computers’?If we understand the basis of our mental self-image, or identity,can we (and should we) seek tochange ourselves into somethingelse? And if our actions are justbiology in action, how responsiblecan we be for what we do?

2|BIG PICTURE 4

Our brains are staggeringly clever things. They can take in incredible amountsof information, ﬁlter out what is not needed, store away information for futurereference, recall past experience, and control what the rest of the body does.

All images, unless otherwise indicated, are fromthe Wellcome Trust’s Medical Photographic Library. The Wellcome Trust is an independentbiomedicalresearch funding charity (registered charity no. 210183). The Trust’s mission is to foster and promote researchwith the aim of improving human and animal health.Reﬂecting the profound impact today’sresearch willhave on society, the Wellcome Trust also seeks to raiseawareness of the medical, ethical and social implicationsof research and promote dialogue between scientists,the public and policy makers.

or ‘how to’ memories(e.g. how to swim or ride a bicycle) are storedin the cerebellum and putamen.

2

Emotional memories

such as those related tophobias and ﬂashbacks are initially encodedin the amygdala, which then inﬂuences othermemory-encoding regions.

3

Episodic memory

is made up of the personalmemories, our ‘ﬁlmic’ recollection of pastexperiences. This is encoded by the hippocampusand stored in the cortex.

4

Semantic memory

is for facts. They are registeredby the cortex and end up in the temporal lobe.We also have an unconscious (or ‘

implicit

’) memory– we may unconsciously react to a stimulusdifferently if we have experienced it before, evenif we are not aware that we have seen it before.

What’s more, they do all these thingssimultaneously, every waking secondof the day.We are just beginning to work out howthe brain manages these incrediblefeats, and how it is that single cells –mainly

neurons

– acting together cando so many wonderful things.

TYPES OF MEMORY

Amygdala:

Emotion

Hypothalamus:

Body physiology(e.g. temperaturecontrol)

Broca’s area:

Speech

Frontalcortex:

Thinking

Hippocampus:

Makingmemories

Motor cortex:

Control ofmovement

Somatosensorycortex:

Touch

Visual cortex:

Vision

Cerebellum:

Unconsciouscontrol, (e.g.posture, balance)

Auditorycortex:

Hearing

LOOKING ANDLEARNING

The brain at work

The brain operates by

divisionof labour

: different areas arespecialised for different functions(see diagram). However, theseare not independent republics –connections between themare equally important.Many insights have come frompeople whose brain injuries havealtered their behaviour. Theclassic case is that of railwayworker

Phineas Gage

. In 1848an explosion blew a metal rodthrough his skull, removing alarge chunk of forebrain. Gagesurvived but his personalitychanged dramatically. Formerly areliable worker, after the accidenthe became a drunken drifter,aggressive and impulsive, hisability to control behaviour lostwith his prefrontal cortex.

Vision is our most crucial sense. We relyon it for survival but just how reliable is it?

It is tempting to think of our eyes as mini-camerasconstantly ﬁlming the outside world. In fact, vision isnothing like that. The seamless view of the world isan illusion created by the brain after it has dismantledthe input it receives from the eyes.For a start, we do not look at a scene in a steadyway. Instead, our eyes constantly ﬂicker back andforth (involuntary movements known as

saccades

),scanning scenes in detail. From this constantlyshifting input, the brain builds up a coherent mentalpicture corresponding to a scene.We now know that neurons in our brain specialisein recognising particular aspects of a scene, suchas edges or dots or motion. Each neuron has a‘

receptive ﬁeld

’, an area around it that is sensitiveto its favoured stimulus (like a detector attached toa security light, which can detect movement withina particular area of ground). Then, in a computational task of staggeringcomplexity, the brain integrates all these signals tocreate a visual impression of the outside world.

Pay attention

Another key difference between the visual systemand a camera is the phenomenon of

attention

. There is so much going on in the world that the brainhas to ﬁlter out unnecessary input. One way it doesthis is by focusing on (or ‘

attending

’) to a small areaat any one time.We are not very aware of this, partly because ourperipheral vision is sensitive to movement, so if something noteworthy happens there we are quick tonotice. But it means we take in much less of a scenethan we might imagine. A nice example is a study in which volunteers wereasked to watch a videotape of people playingbasketball. They were asked to count the passesmade by one of the teams. Afterwards they wereasked if they had noticed anything unusual.Fixated on counting, almost half failed to spot a womandressed in a gorilla suit who stopped to face thecamera, banged her chest and walked off.

Filling in

The other big difference between the brain and acamera is that the brain guesses more. Whenpresented with incomplete information, it ﬁlls in thegaps, making assumptions about what should bethere given the rest of the visual input it is receiving. This

ﬁlling in

can be useful. The visual system isoften trying to extract patterns. So when it ﬁnds onebut with a bit missing, it ﬁlls in the missing space, sowe get a complete coherent picture. But it sometimesleaps to the wrong conclusion. Can we believe oureyes? Not always.

Optical quirk – www.ophtasurf.com/en/bestillusions5.htm

This optical illusion illustrates how our perception can be tricked –in this case into believing something is moving. Optical illusionshave told us much about how the brain interpretsscenes, for more details (and illusions) see...

www.wellcome.ac.uk/bigpicture/thinking

ONT HE W E B

The brain structures, neuronsand even molecules and genesassociated with memory arebeginning to be identiﬁed.

We are in many ways the sum of ourexperiences. How we act and behavedepends not just on what is happeningto us now but also on what hashappened to us in the past. We learnand we can make memories.Nearly all animals can learn. A simpleform of learning is

association

– somekind of sensory stimulus is ‘remembered’and an animal’s behaviour changes thenext time it encounters that stimulus. The classic example is provided by

Pavlov’s dogs

, who were given foodevery time a bell rang. Eventually, theybegan to salivate in response to thebell on its own.Human memory is more complex –in fact, we have several different typesof memory, involving many parts of the brain (see box, below left).

Making memories

But what exactly does a ‘memory’look like in the brain? Again, it isdifﬁcult to liken it to anything everydaysuch as a photograph in an album.Memories are hard to pin down, asthey involve a constellation of neuronsconnecting together in different patterns.Putting away the memory of Christmasday is produced by millions of neuralbrain patterns ﬁring: some for thetaste of Brussels sprouts, others fora favourite carol. The pattern remainsafter the stimulus disappears and amemory is born.In terms of mechanisms, memory makingis thought to depend on neuronsstrengthening their connections to oneanother – ‘remembering’ that they havebeen in touch before (see ﬁgure above).

STRANGE TIMES

Some people with brain damage,or by a quirk of fate, lack a veryspeciﬁc mental function.

Blindsight

Remarkably, some patients haveno conscious vision but can stillpoint at a coloured dot on a screenwhen forced to guess.This suggeststhat we can ‘see’ things withoutbeing consciously aware of them.

Synaesthesia

Some people don’t just hear sounds– they see them too (see page 12).

Prosopagnosia

People with

prosopagnosia

are unable to recognise

faces

,suggesting that there is a ‘module’in the brain speciﬁcally dealingwith face recognition.

When a nerve impulse (green) arrives at the endof a neuron, neurotransmitters ferry the signalacross the synapse (pink), setting off a newaction potential (blue). Signals are also sentback to the original neuron (yellow, top) so thatthe next time a nerve impulse arrives (bottom)the second neuron reads more strongly.